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May 06, 2014

DESERT BLOOM: Emerald Ash Borer



There are so many trees out in the world, but only a relatively small number can survive, much less actually flourish, in our challenging environment. We do insist on growing some poorly fitting ones: looking around the valley, there are lots of marginal purple leaf plums, short-lived chitalpas, and even the occasional weeping willow. When I see those, I get a little incensed, since there’s no excuse for growing them in the middle of the Mojave – they only belong in places that get considerably more than four and a quarter inches of rainfall per year!

MesquiteOf course, true desert trees, like mesquite and desert willow (which is not even remotely related to the weeping one), grow and thrive here.  Even here, though, we do have a bigger selection that just those two. Included in that group are several of the ashes. You can find various kinds of ash trees growing perfectly well all around the country. I recently read that there are over seven billion ash trees growing in the US!

Arizona AshGiven the name, Arizona ash would be an obvious choice for this region, but they’re not alone. Raywood, fan-tex, velvet ash – they all tolerate desert conditions remarkably well, as long as they receive enough water and the occasional hit of compost tea. We have so few great tough shade trees in the desert; we need to keep them healthy and happy.

Not everything is so great for ash trees in this country, unfortunately. There is a pest making its way across the continent, causing devastation in its path. The only good thing about it is that it only affects ash.

This pest is a slender little insect, about ¼ to ½ inch long, colored a vivid green, that destroys ash trees. The emerald ash borer has been marching from east to west, killing its hosts.

Such a small thing, with such a pretty color, and such a terrible villain! From the time it was introduced into the US (not deliberately introduced, obviously), it has killed tens of millions of ash trees. Apparently, it arrived from Asia on packing crates in cargo ships and planes. Since its first sighting in 2002, it spread throughout the northeast and a sizeable chunk of the central United States.

To try and keep it from spreading even more than it already has, certain agencies, including the Department of Agriculture, have imposed quarantines on wood from 21 states and two Canadian provinces. This is one of the few ways to slow down its migration.

Still, it continues to spread, albeit more slowly than it would otherwise.

The difficulty is that people don’t always pay attention. I’m not sure who drew it, but there’s a cartoon that gives a good explanation of how this insect’s been able to continue its lethal journey. In this cartoon, a big man is carrying a bundle of firewood. Strolling next to him is an emerald ash borer wearing a t-shirt that says, “I’m with stupid”.

Ash borer

People who want to save a few dollars frequently carry their own firewood when they go camping. Too often, they’re bringing it from infested states where there’s now lots of dead ash wood, to places where the borer hasn’t yet been established.  

Happily, this bit of misery isn’t in Nevada – yet. Since we need to keep our ash trees alive, all of us should be careful and observant. 

As I said, it’s only up to a half inch long, so the insect itself’d be easy to miss.

It’s not the adult that causes the plant to die, however. Adults eat a few leaves, but don’t kill the tree. Its voracious babies, on the other hand, are the bad guys. If an ash has a D shaped hole in the bark, look closer. A D-shaped hole is the exit for the adults who grew from the juveniles who destroyed part of the tree’s circulatory system.

This is a real concern. If you see this kind of a hole, especially if the ash tree looks stressed, call Cooperative Extension: (702) 222-3130

For KNPR’s Desert Bloom, this is Dr. Angela O’Callaghan of the University of Nevada Cooperative Extension.

See discussion rules.


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